1. Field of The Invention
A mechanical transmission device for modifying torque and speed of rotation from torque input to torque output, more particularly a device capable of modifying torque and speed of rotation in a continuously variable fashion utilizing a single set of levers in conjunction with an abaxial ring.
2. Background Information
To expand the usefulness of rotary power sources, a variety of variable torque transmission and conversion devices have been developed. Among the most energy efficient variable transmission systems are the incrementally shiftable systems that employ multiple gears or chains and cogs, but these systems generally require an interruption in power during shifts, and where many ratios are required they can become complex, bulky, and difficult to manage. Continuously variable transmissions offer greater versatility and simplify shifting operations, but all have limitations which make them more suitable for some applications than others.
The hydraulic or electrical drives, where a motor is driven by a pump or generator, are among the most versatile continuously variable drives, but they tend to be massive and not very energy efficient, so their use has mostly been restricted to heavy industry and high-load work and transport machinery.
Limited slip differential drives employ a split in the torque path with a brake or clutch or something to provide variable drag to select between paths having different ratios. Energy efficiency is good when either path is fully selected, but there are friction losses in all intermediate positions and the intermediate ratios tend to be unstable because the constancy of a given ratio is only as good as the proportionality between the friction and the power load.
Traction drivesxe2x80x94where a ring, disk, or belt frictionally engages a disk, cone, or sphere at varying radiixe2x80x94have stable ratios throughout their range and are often more energy efficient than limited-slip drives in the intermediate ratios, but the power is transmitted through a rolling frictional interface. This interface can slip if the shear load from the power exceeds the friction, and it tends to be a focal point for wear and energy loss problems.
Potentially some the most energy efficient of the continuously variable drives are the oscillation drives, where rotary power is converted to oscillating power and then back again to rotary power and variable gearing is achieved by varying the amplitude of the oscillations. Rotary power loses directionality when converted to oscillating power, so there is usually a directional freewheeling mechanism which imparts directionality when converting back to rotary power, so reversing the direction of the input rotary power will typically not reverse the direction of the output rotary power; and most oscillation drives are not symmetrical such that the roles of input and output elements can be swapped. To have continuous power transmission, there must be at least two oscillating elements, each to take the load while the other is returning. Also, oscillation drives tend not to be very compact. However, oscillation drives have stable ratios and they can entirely eliminate the frictional rolling interfaces that traction drives require, so the efficiency and durability can be good. The main design challenges of the oscillation drives have been to have the oscillating elements receive and deliver power as tangentially as possible to the rotary elements while keeping the total number of elements as few as possible.
The device of this application is a rotary transmission device with some, but not all, of the properties of a typical oscillation drive. Like most oscillation drives, the output power is unidirectional, and reversing the direction of rotary input power will merely freewheel the input torque element rather than drive the output element in reverse. Unlike most oscillation drives, however, applicants device is symmetrical in that it is arbitrary which is the drive element and which is the driven element. If applicants device is flipped end-for-end, it will operate to convert torque identically.
Applicants torque transmission device has utility, for example where an unlimited number of stable gear ratios over a certain range is of benefit and where high efficiency, reasonable simplicity, and compactness are desired. This can have applications in diverse areas including pumps (giving non-variable displacement pumps variable output); endless double-loop chain hoists; machinery and conveyance timing; mopeds and other low-power vehicles that currently employ belts and expandable pulleys; and many forms of human-powered vehicles. Probably the most familiar and common of these machines is the bicycle, so for purposes of illustration, this device is herein described with particular reference to bicycles with the understanding that it can have uses for other machines as well.
Despite several attempts to give bicycles continuously variable transmissions, virtually all contemporary multi-speed bicycles still shift in discrete steps; that is, they experience a jump in gearing when shifting from one gear ratio to another. An advantage is seen in having a torque transmission device which can operate on bicycles as they exist without requiring extensive modification of the basic bicycle form; which has energy efficiency similar to that of existing multi-speed drives; which drives when pedalling forward and freewheels when pedalling backward; which permits coasting (rolling without the application of power); which is compact and reasonably lightweight; and importantly, which can provide an unlimited number of stable gear ratios, continuously selectable over a finite range, which can be selected at any time whether stopped, coasting, or pedalling. Applicant proposes the device of this application as such a device.
Applicant""s invention employs a rotating torque input element such as a drive ring or shaft on a primary axis (the primary axis being an arbitrary reference axis which may be coincident with the axis of a wheel, pulley, crank, gear, or any other rotatable element for delivering or receiving torque); a rotating torque output element such as a ring or shaft, also on the primary axis; a multiplicity of levers radiating from the primary axis, each rotatable about the primary axis; means by which to engage and disengage each lever with the input and output elements; an abaxial element such as a ring rotating on a secondary axis parallel to, but not coincident with the primary axis; and means by which to engage the abaxial element with each of the multiplicity of radiating rotatable levers and means to move abaxial with respect to the primary axis.
The multiple rotating levers bear, in succession, the input torque load from the drive element. The multiple rotating levers deliver, in succession, the output torque load to the driven element. Each lever will engage the driving and driven elements at different times through a rotation about the primary axis, with an unloaded cycle between each duty. Succession of load on the levers is determined by speed of rotation so that only the slowest and fastest rotating levers bear a load at any time. The load is conducted between the slowest and fastest levers via an abaxial ring, and it is by this ring acting on differing radii of these levers that modification of torque is achieved.
The principle of this torque converter is unaffected by the position of the devices on each lever which engage the input and output elements, but since loads and engagement lag times are reduced as the distance from the axis of rotation is increased, an advantage is seen in having the engagement devices, such as clutches, located away or distal from the axial end of each lever. The drive and driven elements will have radii corresponding to the position of their respective clutches, and so will typically take the form of disks or rings (hereafter referred to as the drive and driven rings).
This torque converter device functions the same whether the bearings for rotation are mounted within a housing or on an axle, but an advantage in terms of versatility and economy of design is seen in mounting the assembly on an axle. Further, the clutches can operate to obtain either an increase or decrease in torque with a corresponding decrease or increase in speed of rotation, respectively. If the fastest lever engages the drive ring and the slowest lever engages the driven ring, torque will be increased and speed will be decreased. If the slowest lever engages the drive ring and the fastest lever engages the driven ring, torque will be decreased and speed will be increased. For simplicity, the preferred embodiment utilizes directional clutches which engage and disengage according to the relative motion between the levers and the drive and driven rings. In this configuration, torque will be delivered from the slowest lever to the fastest lever, resulting in an increase in speed and a decrease in torque to the output elements, such as a wheel.